1. Field of the Invention
The present invention relates generally to hearing systems and methods. More particularly, the invention is directed to hearing systems and methods that rely on electromagnetic fields to produce vibrations on a portion of the human ear. Such systems may be used to enhance the hearing process with normal or impaired hearing.
Presently, most hearing systems fall into at least three categories: acoustic hearing systems, electromagnetic drive hearing systems, and cochlear implants. Acoustic hearing systems rely on acoustic transducers that produce amplified sound waves which, in turn, impart vibrations to the tympanic membrane or eardrum. The telephone earpiece, radio, television and aids for the hearing impaired are all examples of systems that employ acoustic drive mechanisms. The telephone earpiece, for instance, converts signals transmitted on a wire into vibrational energy in a speaker which generates acoustic energy. This acoustic energy propagates in the ear canal and vibrates the tympanic membrane. These vibrations, at varying frequencies and amplitudes, result in the perception of sound. Surgically implanted cochlear implants electrically stimulate the auditory nerve ganglion cells or dendrites in subjects having profound hearing loss.
Hearing systems that deliver audio information to the ear through electromagnetic transducers are well known. These transducers convert electromagnetic fields, modulated to contain audio information, into vibrations which are imparted to the tympanic membrane or parts of the middle ear. The transducer, typically a magnet, is subjected to displacement by electromagnetic fields to impart vibrational motion to the portion to which it is attached, thus producing sound perception by the wearer of such an electromagnetically driven system. This method of sound perception possesses some advantages over acoustic drive systems in terms of quality, efficiency, and most importantly, significant reduction of “feedback,” a problem common to acoustic hearing systems.
Feedback in acoustic hearing systems occurs when a portion of the acoustic output energy returns or “feeds back” to the input transducer (microphone), thus causing self-sustained oscillation. The potential for feedback is generally proportional to the amplification level of the system and, therefore, the output gain of many acoustic drive systems has to be reduced to less than a desirable level to prevent a feedback situation. This problem, which results in output inadequate to compensate for hearing losses in particularly severe cases, continues to be a major problem with acoustic type hearing aids. To minimize the feedback to the microphone, many acoustic hearing devices close off, or provide minimal venting, to the ear canal. Although feedback may be reduced, the tradeoff is “occlusion,” a tunnel-like hearing effect that is problematic to most hearing aid users. Directly driving the eardrum can minimize the feedback because the driving mechanism is mechanical rather than acoustic. Because of the mechanically vibrating eardrum, sound is coupled to the ear canal and wave propagation is supported in the reverse direction. The mechanical to acoustic coupling, however, is not efficient and this inefficiency is exploited in terms of decreased sound in the ear canal resulting in increased system gain.
One system, which non-invasively couples a magnet to tympanic membrane, is disclosed by Perkins et al. in U.S. Pat. No. 5,259,032, incorporated herein by reference. The above-mentioned patent discloses a device for producing electromagnetic signals having a transducer assembly which is weakly but sufficiently affixed to the tympanic membrane of the wearer by surface adhesion. U.S. Pat. No. 5,425,104, also incorporated herein by reference, discloses a device for producing electromagnetic signals incorporating a drive means external to the acoustic canal of the individual. However, because magnetic fields decrease in strength as the reciprocal of the square of the distance (1/R2), previous methods for generating audio carrying magnetic fields are highly inefficient and are thus not practical. At the present, there is considerable room for improvement in the delivery of electromagnetic fields sufficient to efficiently drive a transducer coupled to an acoustic member of an individuals ear.
For these reasons it would be desirable to provide an improved hearing system, which delivers electromagnetic fields to a transducer, that is coupled to an acoustic member of an individual's ear sufficiently to drive the transducer with minimal power. It would further be desirable to provide a hearing system leaving an open channel in the ear canal to minimize occlusion. At least some of these objectives will be met by the inventions described hereinafter.
2. Description of the Background Art
U.S. Pat. Nos. 5,259,032 and 5,425,104 have been described above. Other patents of interest include: U.S. Pat. Nos. 5,015,225; 5,276,910; 5,456,654; 5,797,834; 6,084,975; 6,137,889; 6,277,148; 6,339,648; 6,354,990; 6,366,863; 6,387,039; 6,432,248; 6,436,028; 6,438,244; 6,473,512; 6,475,134; 6,592,513; 6,603,860; 6,676,592; and 6,695,943. Other publications of interest include: U.S. patent Publication Nos. 2002-0183587, 2001-0027342; Journal publications Decraemer et al. (1994), Puria et al. (1997), Moore (1998), Puria and Allen (1998), Fay et al. (2002), and Hato et al. (2003).